Membrane Pump and Method for Adjusting Same

ABSTRACT

The present invention concerns a pump adjusting method and a membrane pump having a pumping chamber, a pressure and a suction connection, wherein the pressure and the suction connections are connected to the pumping chamber, a hydraulic chamber, wherein the pumping chamber and hydraulic chamber are separated from each other by a membrane, wherein a pulsating working fluid pressure can be applied to the hydraulic chamber which can be filled with a working fluid, wherein the membrane is moved between a first and second chamber positions of different volumes, wherein the chamber is connected to a working fluid reservoir, wherein the membrane comprises exchangeable spring elements exerting different forces on the membrane. The force which is exerted by the spring element on the membrane in the direction of the second position can be adjusted.

The present invention relates to a membrane pump and to a method foradjusting a membrane pump.

Membrane pumps generally comprise a pumping chamber separated from ahydraulic chamber by a membrane, wherein the pumping chamber isconnected to a suction connection and a pressure connection. A pulsatingworking fluid pressure can be applied to the hydraulic chamber, whichcan be filled with working fluid. The pulsating working fluid pressurebrings about a pulsating movement of the membrane, whereupon the volumeof the pumping chamber expands and contracts periodically. In thismanner, the pumping medium can be sucked in via the suction connection,which is connected to the pumping chamber via a respective non-returnvalve, when the volume of the pumping chamber is expanded, anddischarged underpressure via the pressure connection, which is alsoconnected to the pumping chamber by means of a respective non-returnvalve, when the volume of the pumping chamber contracts.

As a rule, the working fluid is a hydraulic oil. In principle, however,other suitable fluids can be used, such as water with a water-solublemineral supplement, for example.

The membrane separates the medium to be pumped from the drive, whereuponon the one hand the drive is protected from damage caused by the pumpingmedium and on the other hand, the pumping medium is also protected fromdamage, for example contamination, caused by the drive.

The pulsating working fluid pressure is usually produced by means of amovable piston which is in contact with the working fluid.

To this end, for example, the piston is moved to and fro in acylindrical hollow element, whereby the volume of the hydraulic chamberis expanded and contracted, resulting in increasing and decreasing thepressure in the hydraulic chamber and, as a result, in movement of themembrane.

Despite a very wide variety of measures aimed at preventing the workingfluid from flowing around the piston, in practice it is not possible toprevent a small quantity of the working fluid from being lost on eachstroke through the narrow gap that remains between the piston on the onehand and the cylindrical hollow element on the other hand, and sogradually, the amount of working fluid in the hydraulic chamber isreduced. This results in the fact that the pressure stroke is no longercompleted by the membrane, since there is no longer sufficient workingfluid available to execute the compression movement of the membrane.

As an example, then, DE 1 034 030 proposed connecting the hydraulicchamber via an interposed valve, a so-called leakage compensation valve,to a reservoir of working fluid.

By means of this leakage compensation valve, working fluid can be addedto the hydraulic chamber as necessary. However, care must be taken whendoing this not to add too much working fluid to the hydraulic chamber asthen, the membrane would move too far into the pumping chamber duringthe pressure stroke and under some circumstances might come into contactwith valves or other components and be damaged.

For this reason, the leakage compensation valve usually comprises aclosing body, for example in the form of a closing ball, which can moveto and fro between a closed position in which the valve gate is closedand an open position in which the valve gate is open. This closing bodyis biased into the closed position with the aid of a pressure element,for example a spring. This pressure element is designed such that theclosing body only moves in the direction of the open position when thepressure in the hydraulic chamber is lower than a set pressure p_(L). Inorder to prevent the leakage compensation valve from opening too soonduring the suction stroke, i.e. while the piston moves backwards andthus the volume in the hydraulic chamber is expanding, the membrane isfrequently provided with a spring element which is in turn designed suchthat it exerts a force on the membrane so that the membrane is biased inthe direction of the hydraulic chamber. In this manner, the springelement assists the movement of the membrane in the direction of itssuction stroke.

Normally, pressure pumps are required to run for a predetermined time,usually 5000 to 10000 service hours, without maintenance or repair.

In order to ensure this, it must be ensured that the working zone of themembrane always follows the motion of the piston and stays within thedome chamber provided for it, which dome chamber is formed by thepumping chamber and the hydraulic chamber.

If, therefore, for some reason too much working fluid gets into thehydraulic chamber, the membrane will move away from the piston movementin the pressure stroke direction, with the result that before the pistonhas completed the pressure stroke, it impinges on the walls of thepumping chamber and is perforated on the bores leading to the valves.

Since perforation leads to breakdown of the membrane pump, it isessential that this should be avoided.

It is thus extremely important that the dimensions of the leakagecompensation valve be such that it only opens when the membrane becomesseated on the hydraulic side dome at the end of the suction stroke. Thiscauses a brief under-pressure, whereupon the spring-loaded leakagecompensation valve opens and the hydraulic chamber is supplemented withthe exact quantity of working fluid that is missing.

The danger of perforating the membrane always arises if the leakagecompensation valve opens before the membrane has reached its boundaryposition on the hydraulic side. To avoid this, the pressure in thehydraulic chamber during the suction stroke may only drop below the setpressure of the leakage compensation valve if the membrane is seated onthe dome.

Furthermore, when the pump is stopped, even when an under-pressuredevelops in the pumping chamber, the pressure in the hydraulic chamberhas to be at least 1 bar (=atmospheric pressure), since otherwise,because of the leaks that are always present, the membrane would move inthe direction of the pressure stroke and small quantities of fluid wouldflow in, either via the pistons or via the leakage compensation valve,which would lead to perforation of the membrane upon start-up of thepump.

In order to satisfy this condition every time, EP 1 291 524 proposesthat the spring force be set such that in the suction stroke, themembrane also follows the piston if there is a vacuum in the pumpingchamber, i.e. the pressure applied to the working fluid by the springforce via the membrane is always more than 1 bar. The pressure onlydrops when, at the end of the suction stroke, the membrane is at thehydraulic side end of the dome, since the membrane can then no longerfollow the piston. At that moment, working fluid can be added via theleakage compensation valve if necessary.

Since the force F on the membrane due to the pressure difference isproportional to the square of the diameter D of the membrane, but at thesame time the shear and bending forces applied to the surface at theclamping rims of the membrane are only proportional to the diameter, theshear stress increases proportionally to the diameter of the membrane D;thus, particularly with large membrane pumps, this can lead tooverloading of the membrane and subsequently to breakage of the membranebefore the expiry of the envisaged operational lifetime.

Since the increase in the spring force F is proportional to D², withlarge diameter membranes a pressure of at least 1 bar requires verystrong and thus expensive springs. As an example, a membrane diameter of100 mm requires a spring force of 750N, whilst a membrane diameter of400 mm already requires one of 12000 N.

Starting from the prior art described, the aim of the invention is toprovide a membrane pump and a method for adjustment thereof, by means ofwhich the problems discussed above can be reduced or even completelyovercome.

Regarding the membrane pump, this is accomplished by means of a membranepump with a pumping chamber, a pressure and a suction connection,wherein the pressure and the suction connections are connected to thepumping chamber, a hydraulic chamber, wherein the pumping chamber andhydraulic chamber are separated from each other by a membrane, wherein apulsating working fluid pressure can be applied to the hydraulic chamberwhich can be filled with a working fluid, wherein the membrane is movedbetween a first position in which the pumping chamber has a smallvolume, and a second position, in which the pumping chamber has a largervolume, and the hydraulic chamber is connected to a working fluidreservoir via a leakage compensation valve, wherein the membranecomprises a spring element, which is designed such that it exerts afirst predetermined force on the membrane in the direction of the secondposition. In accordance with the invention, the spring element can beexchanged for another spring element which is designed such that itexerts a second predetermined force on the membrane in the direction ofthe second position, or the force which is exerted by the spring elementon the membrane in the direction of the second position can be adjusted.

Because of the adjustability or exchangeability of the spring element,the spring force can be matched to the prevailing conditions, such asthe static pressure at the suction connection. If, for example, it isestablished for the desired use that the static pressure at the suctionconnection itself is already 1 bar and a suction valve which connectsthe suction connection to the pumping chamber is designed such that itopens at a pressure difference of more than 0.3 bar, then the pressurein the pumping chamber cannot fall below 0.7 bar. Consequently, thespring element too must only exert a smaller force on the membrane,which further increases the service life of the membrane.

Thus, in accordance with the invention, the spring force of the springelement can be matched to local circumstances.

In accordance with a preferred embodiment, the spring element can bedetached from the membrane. Thus, the spring element can be changedwithout having to change the membrane. However, in principle it is alsopossible for the membrane itself to have appropriate resilientproperties.

Furthermore, it may be advantageous for a hydraulic body and a membranebody to be provided between which the membrane is clamped such that thehydraulic chamber is disposed in the hydraulic body and the pumpingchamber is arranged in the membrane body, wherein the hydraulic bodycomprises a closeable opening arranged in the direction of force of thespring element through which the spring element can be changed or itsspring constant can be adjusted. In general, the drive piston isdisposed behind the spring element in the direction of force, so thatchanging or adjusting the spring element is only possible by means ofextremely time-consuming dismantling of the pump. The closeable openingof the invention means that now, after the pump has been assembled andthe static pressure has been established at the suction connection, thespring constant can easily be adjusted to the conditions. In principle,it would also be possible to dispose the spring element in the pumpingchamber. In this case, it would be advantageous for the membrane body tocomprise a closeable opening disposed in the direction of force of thespring element, through which the spring element can be changed oradjusted.

In a further preferred embodiment, the pulsating working fluid issupplied to the hydraulic chamber via a channel, wherein the channel isorientated, at least in the region of its opening into the hydraulicchamber, such that it forms an angle a with the direction of force ofthe spring element which is more than 0°, preferably more than 45°,particularly preferably more than 70° and most preferably approximately90°. Because this results in a lateral supply of pulsating working fluidto the hydraulic chamber, there is sufficient space to gain access tothe spring element in order to adjust it or change it “from the back”,i.e. from the side facing away from the membrane.

Regarding the method for adjusting a membrane pump, the above-mentionedaim is achieved by providing a step wherein the spring constant isselected or adjusted such that the pressure p_(FV) applied to theworking fluid by the spring element via the membrane is:p_(FV)>p_(A)−p_(SO), where p_(A) is the atmospheric pressure and p_(SO)is the static pressure at the suction connection.

In a further preferred embodiment, the pressure p_(FV) applied to theworking fluid by the spring element is selected such that

p _(A) >p _(FV) >p _(A) −p _(SO).

This ensures that the hydraulic chamber is not supplied with too muchworking fluid via the leakage compensation valve. However, the forceapplied to the working fluid by the spring element can be selected so asto be substantially smaller than it is usually the case in the prior artsince, in accordance with the invention, it is for the first timeallowed for that a static pressure is applied to the suction connectionsuch that as a rule, a lower pressure cannot exist in the pumpingchamber.

Since in some embodiments the suction connection is connected to thepumping chamber via a non-return valve, which also has an appropriatespring element such that the non-return valve only opens when there is apressure difference Δp_(SV) between the pressure at the suctionconnection and the pressure in the pumping chamber, in a preferredembodiment, the pressure p_(FV) applied to the working fluid by thespring element is set so that the following holds:p_(A)>p_(FV)>p_(A)−p_(SO)+Δp_(SV).

In a further preferred embodiment, the hydraulic chamber is connected toa working fluid reservoir via a leakage compensation valve, wherein theleakage compensation valve comprises a closing body which is movable toand fro between a closed position in which the valve gate is closed andan open position in which the valve gate is open, which closing body isheld in the closed position with the aid of a pressure element, whereinthe pressure element is designed such that if the pressure in thehydraulic chamber is lower than a set pressure p_(L), the closing bodymoves in the direction of the open position. Advantageously, thepressure element of the leakage compensation valve and the springelement of the membrane are constructed and arranged such that at anytime the sum of the pressure p_(H) in the hydraulic chamber and thepressure p_(FV) applied by the spring element to the working fluid ishigher than the set pressure p_(L).

In a further preferred embodiment, the mass of the closing body is suchthat the closing body moves by not more than 0.2 mm, preferably not morethan 0.1 mm, in the direction of the open position when a pressure dropto 0 bar which lasts no longer than 1 ms occurs as a result of apressure pulse in the hydraulic chamber.

Further advantages, features and possible applications will becomeapparent from the following description of a preferred embodiment andfrom the accompanying drawings, which show:

FIG. 1: a diagrammatic sectional view of a membrane pump head inaccordance with the invention;

FIG. 2: an illustrative diagram of the pressure in the hydraulic chamberover time; and

FIG. 3: a sectional view of a specially designed leakage compensationvalve.

FIG. 1 shows a detail of a membrane pump head in a sectional view. Themembrane pump comprises a membrane 1, which is clamped between ahydraulic body 23 and a membrane body 22. The membrane divides thedome-shaped cavity into a pumping chamber 9 and a hydraulic chamber 8.The membrane 1 is connected by a screw connection with a bolt which ispulled into the hydraulic body with the aid of a spring element 10. Inother words, the spring element 10 exerts a force on the membrane 1 inthe direction of the hydraulic chamber 8.

The pumping chamber 9 is connected to a suction connection (not shown)and a pressure connection (not shown) via appropriate valves. Anoscillating hydraulic pressure can be applied to the membrane 1 via thechannel 24. If the pressure rises in the channel 24, the membrane 1 inFIG. 1 is moved to the left, i.e. the pumping chamber 9 is contracted.Any pumping medium therein is then forced out of the pressure connectionvia the valve. If the pressure in the channel 24 is then reduced, thenthe spring element 10 ensures that the membrane is drawn back into thehydraulic chamber. The pressure in the pumping chamber 9 will fall untilit is lower than the static pressure at the suction connection. Thenpumping medium is fed via the suction connection into the pumpingchamber 9.

By means of the periodic movement of the membrane, then, pumping mediumis periodically drawn out of the suction connection and discharged viathe pressure connection at a higher pressure. The membrane is heldbetween the clamping rims 11, 12. The spring element 10 might cause themembrane 1 to bulge.

During operation, under certain circumstances, working fluid escapes viathe piston because of leaks brought about by the pulsating working fluidpressure. In order to ensure that the right quantity of working fluid ispresent in the hydraulic chamber 8, a leakage compensation valve 6 isprovided, via which the hydraulic chamber 8 is connected to a workingfluid reservoir. This leakage compensation valve 6 comprises a smallball 16, which is urged into a valve seat by means of a spring 17. Thespring 17 of the leakage compensation valve 6 establishes a set pressurep_(L). If the pressure in the hydraulic chamber 8 drops below this setpressure p_(L), the ball of the leakage compensation valve lifts fromthe valve seat and additional working fluid can flow from the workingfluid reservoir 15, which is generally under atmospheric pressure (1bar), into the hydraulic chamber 8 until the pressure in the hydraulicchamber 8 has risen above the set pressure p_(L) since then the springof the leakage compensation valve 6 urges the ball back into the valveseat and thus closes off the valve gate.

In the embodiment shown, an opening is provided in the hydraulic element23, which can be closed with the aid of the cap 21. If the cap 21 isremoved from the hydraulic body, then the spring element 10 can beaccessed. In this manner, the spring element can easily be exchanged orre-set, in order to ensure that as little force as possible is appliedto the membrane via the spring element 10, at the same time howeverensuring that the leakage compensation valve 6 only opens when needed.This ready accessibility is made possible because the pulsating workingfluid is supplied via the channel 24 which is arranged essentially at a90° angle to the direction of force of the spring element 10.

FIG. 2 graphically shows the pressure in the hydraulic chamber duringthe suction stroke as a function of time. At the start of the suctionstroke, the pressure in the hydraulic chamber is approximately the sameas the pressure with which the pump discharges the pumping medium fromthe pressure connection. This pressure is substantially higher than thestatic pressure of the suction line. It should be understood that thepressure in the hydraulic chamber is also determined by the returnspring 10.

The suction stroke begins when the piston is moved back in order toproduce the pulsating working fluid pressure. Initially, this means thatthe pressure in the hydraulic chamber reduces slowly and since thepressure in the pumping chamber is higher, the membrane moves to theright, i.e. in the direction of the hydraulic chamber. Here, thepressure in the pumping chamber will drop slowly, until it reaches thestatic pressure at the suction connection p_(SO). If the pressure dropsstill further, the respective non-return valve which connects thepumping chamber to the suction connection will open and pumping mediumwill flow via the suction connection. At the moment at which thepressure in the pumping chamber reaches the static pressure at thesuction connection, an abrupt change in the velocity of the fluid occursin the suction line. This change in velocity ΔV gives rise to theso-called Joukowsky pulse, Δp_(ST)=ρ×a×ΔV, wherein ρ is the density ofthe pumping medium and “a” is the rate of wave propagation in thefluid-filled suction pipe. This Joukowsky pulse in the pumping chamberresults in a pressure pulse in the hydraulic chamber, since bothchambers are connected via the membrane. The high frequency, rapidlyfading pressure wave can initially be ignored for the followingdiscussion.

The backwards movement of the piston makes the pressure in the hydraulicchamber fall. Thus, with the aid of the spring element 10, sufficientforce has to be exerted on the working fluid in the hydraulic chamber sothat the pressure in the hydraulic chamber does not drop below the setpressure of the leakage compensation valve, as otherwise the leakagecompensation valve would open and additional working fluid would besupplied to the hydraulic chamber.

Known membrane pumps are thus equipped with appropriate return springs10, which ensure that in all cases, the pressure in the hydraulicchamber is higher than the set pressure. Since the pressure in thepumping chamber cannot drop below zero and the pressure in the workingfluid reservoir is typically below atmospheric pressure (1 bar), thesprings are selected so that even at the end of the suction stroke, i.e.when the spring has drawn the membrane to its turning point in thehydraulic chamber, it is more than 1 bar. This ensures that even in theworst case, no unplanned opening of the leakage compensation valveoccurs.

In accordance with the invention, however, it is ensured that the forceexerted by the return spring 10 on the membrane is adjustable, sincemembrane pumps are usually employed in an environment in which a staticpressure p_(SO) is exerted at the suction connection which is greaterthan zero. Depending on which pressure is applied in this case, then,the spring force can be reduced in order to prevent the membrane frombeing drawn unnecessarily strongly into the hydraulic chamber by thespring element 10. The lower the set force, the longer is the servicelife of the membrane. In addition, the drive of the pump can also bereduced, since it only has to work against a small spring force of thespring element 10.

By means of the inventive adjustment of the force applied to themembrane by the spring element 10, then, the energy consumption of themembrane pump can be substantially reduced.

Later on, if the membrane pump has to be adjusted to another staticpressure on the intake line, then the spring element 10 only has to beadjusted or replaced by another one.

The configuration of the invention makes this possible without greatexpense.

As already mentioned, after a certain time from the beginning of thesuction stroke “s”, the pressure p_(H) in the hydraulic chamber dropsabruptly for a brief interval of time (Δp_(ST)). Shortly thereafter, itrises again sharply so that a high frequency, rapidly fading pressureoscillation occurs (Joukowsky pulse). It will immediately be seen thatthe maximum pressure pulse could result in a drop to p=0. However, thepressure in the hydraulic chamber will not actually drop to zero, but toa minimum pressure p_(min), which is set by the operational parametersand the construction of the membrane pump.

Because of this brief drop in the pressure, the pressure might dropbelow the set pressure p_(L), so that the leakage compensation valveopens.

In order to prevent opening upon a pressure pulse drop to p_(min), inthe prior art, it is usual to select the set pressure of the leakagecompensation valve so that p_(L)<p_(min). However, this has the resultthat appropriate constructive measures have to be taken to ensure thatat the end of the suction stroke, the pressure will actually drop belowthe set pressure of the leakage compensation valve when too littleworking fluid is contained in the hydraulic chamber. This increases thecosts of the membrane pump.

Thus, it is proposed that the mass of the closing element of the leakagecompensation valve be raised so that a pressure pulse for a period of upto 1 ms is not sufficient to move the closing body by more than 0.1 mm.

These inventive measures mean, however, that the set pressure p_(L) canbe selected to be substantially higher than p_(min) as long as p_(L) isbelow a mean pressure p_(m) in the hydraulic chamber.

The invention is based on the fact that the pressure pulse occurs overonly a very brief time interval Δts<1 millisecond.

In accordance with the invention, the mass of the closing body isselected to be sufficiently large such that such a pressure pulse onlyresults in a lift of less than 0.2 mm or, preferably, less than 0.1 mm.

An appropriate leakage compensation valve is shown in FIG. 3.

This leakage compensation valve comprises a closing body 16 accommodatedin a valve body 18, which comprises a closing element 20 which closes abore in the valve body 18 in the closed position, so that the line tothe working fluid reservoir 19 is separated from the hydraulic chamber8. The closing body is biased into the closed position with the aid of aspring element 17, as shown in FIG. 3. The pressure of the working fluidin the working fluid reservoir, and thus also the pressure in the line19, remain essentially constant. When the pressure in the hydraulicchamber 8 drops below the set pressure p_(L), which is essentiallyprovided by the spring 17, then the closing body 16 in the positionshown in FIG. 3 is moved upwards, so that a connection is opened betweenthe line 19 and the hydraulic chamber 8.

In principle, it is assumed that if the closing body moves by only 0.2millimetres, the gap between the valve body 18 and the closing element20 is not sufficient to discharge a significant quantity of workingfluid through the line 19 into the hydraulic chamber.

The stroke of the closing body, Δs, is calculated as follows:

$\begin{matrix}{{\Delta \; s} = {b \cdot \frac{\Delta \; t^{2}}{2}}} & (1)\end{matrix}$

where Δt is the duration of the pressure pulse and b is the accelerationof the closing body due to the pressure pulse. The acceleration iscalculated as follows:

b=F/m   (2)

wherein F is the force on the closing body and m is the mass of theclosing body. Thus, we have:

$\begin{matrix}{{{\Delta \; s} = {\frac{F}{m} \cdot \frac{\Delta \; t^{2}}{2}}}{or}} & (3) \\{m = {\frac{\Delta \; t^{2}}{2\Delta \; s} \cdot F}} & (4)\end{matrix}$

Assuming that the pressure pulse does not last longer than 1millisecond, i.e. Δt_(s)=1 millisecond, that the movement of the closingbody should be a maximum of 0.1 mm, i.e. Δs_(s)=0.1 mm, and that thepressure pulse reduces the pressure to 0 bar, i.e. the pressure pulse isthe same magnitude as the set pressure p_(L), i.e. 0.7 bar, then for adiameter of the closing element of 8 mm, i.e. a corresponding surfacearea of about 0.5 cm²:

F=p _(L) ·A=0.7·10·0.5=3.5 N   (5)

and thus

$\begin{matrix}{m = {{3.5 \cdot \frac{10^{- 4}}{2.10^{- 4}}} = {{1.75~10^{- 2}\mspace{14mu} {kg}} \equiv {17.5\mspace{14mu} g}}}} & (6)\end{matrix}$

In the example shown, then, the mass of the closing body has to be atleast 17.5 g in order to prevent a movement of the closing body by morethan 0.1 mm.

If the mass of the closing body is selected so as to be of thismagnitude, then even a pressure pulse to 0 bar will not move the closingbody so far that a significant quantity of working fluid will bereleased into the hydraulic chamber.

The method described may be further improved by considering that thepressure pulse generally does not result in a pressure drop to 0 bar,but only to a minimum pressure p_(min). In equation (5) above, then,instead of the set pressure p_(L), the difference p_(L)−p_(min) betweenthe set pressure p_(L), and the minimum pressure p_(min) due to thepressure pulse can be used, whereupon the mass can be reduced stillfurther. Alternatively, the set pressure p_(L) can be increased,whereupon the spring 17 can be made weaker, simplifying operation of thepump.

LIST OF REFERENCE NUMERALS

-   1 membrane-   6 leakage compensation valve-   8 hydraulic chamber-   9 pumping chamber-   10 spring element-   11, 12 clamping wheels-   15 working fluid reservoir-   16 ball-   17 spring-   18 valve body-   19 line-   20 closing element-   21 cap-   22 membrane body-   23 hydraulic body-   24 channel

1. A membrane pump with a pumping chamber; a pressure and a suctionconnection, wherein the pressure and the suction connections areconnected to the pumping chamber; a hydraulic chamber, wherein thepumping chamber and hydraulic chamber are separated from each other by amembrane, wherein a pulsating working fluid pressure can be applied tothe hydraulic chamber which can be filled with a working fluid, whereinthe membrane is moved between a first position in which the pumpingchamber has a smaller volume, and a second position, in which thepumping chamber has a larger volume, wherein the hydraulic chamber isconnected to a working fluid reservoir via a leakage compensation valve,wherein the membrane comprises a spring element having a first springconstant, which is designed such that it exerts a first predeterminedforce on the membrane in the direction of the second position;characterized in that the spring element can be exchanged for anotherspring element which is designed such that it exerts a secondpredetermined force on the membrane in the direction of the secondposition, or the force which is exerted by the spring element on themembrane in the direction of the second position can be adjusted.
 2. Amembrane pump according to claim 1, characterized in that the springelement can be detached from the membrane.
 3. A membrane pump accordingto any one of claims 1 and 2, characterized in that a hydraulic body anda membrane body are provided, between which the membrane is clamped,such that the hydraulic chamber is disposed in the hydraulic body andthe pumping chamber is disposed in the membrane body, wherein thehydraulic body comprises a closeable opening disposed in the directionof force of the spring element, through which the spring element can bechanged or adjusted.
 4. A membrane pump according to one of claims 1 to2, characterized in that the pulsating working fluid is supplied to thehydraulic chamber via a channel, wherein the channel is orientated, atleast in the region of its opening into the hydraulic chamber, such thatit forms an angle α with the direction of force of the spring elementwhich is >0°, preferably >45°, particularly preferably >70° and mostpreferably approximately 90°.
 5. A membrane pump according to one ofclaims 1 to 2, characterized in that the hydraulic chamber is connectedto a working fluid reservoir via a leakage compensation valve, whereinthe leakage compensation valve comprises a closing body which is movableto and fro between a closed position in which the valve gate is closedand an open position in which the valve gate is open, which closing bodyis held in the closed position with the aid of a pressure element,wherein the pressure element is designed such that if the pressure inthe hydraulic chamber is lower than a set pressure p_(L), the closingbody moves in the direction of the open position.
 6. A membrane pumpaccording to claim 5, characterized in that the pressure element of theleakage compensation valve and the spring element of the membrane areconstructed and arranged such that at any time the sum of the hydraulicchamber pressure p_(H) and the force p_(FV) applied by the springelement to the working fluid is higher than the set pressure p_(L).
 7. Amembrane pump according to claim 6, characterized in that the mass ofthe closing body (16) is such that the closing body (16) moves by notmore than 0.2 mm, preferably not more than 0.1 mm, in the direction ofthe open position when a pressure drop to 0 bar which lasts no longerthan 1 ms occurs as a result of a pressure pulse in the hydraulicchamber (8).
 8. A method for adjusting a membrane pump having a pumpingchamber; a pressure and a suction connection, wherein the pressure andthe suction connections are connected to the pumping chamber; ahydraulic chamber, wherein the pumping chamber and hydraulic chamber areseparated from each other by a membrane, wherein a pulsating workingfluid pressure can be applied to the hydraulic chamber which can befilled with a working fluid, wherein the membrane is moved between afirst position in which the pumping chamber has a smaller volume, and asecond position, in which the pumping chamber has a larger volume,wherein the hydraulic chamber is connected to a working fluid reservoirvia a leakage compensation valve; wherein the membrane comprises aspring element having a first spring constant, which is designed suchthat it exerts a force on the membrane in the direction of the secondposition, characterized in that, the spring constant is selected suchthat for the pressure p_(FV) applied to the working fluid by the springelement via the membrane it holds that: p_(FV)>p_(A)−p_(SO), where p_(A)is the atmospheric pressure and p_(SO) is the static pressure at thesuction connection.
 9. A method according to claim 8, characterized inthat the spring element is selected such that for the pressure p_(FV)applied by the spring element to the working fluid it holds that:p_(A)>p_(FV)>P_(A)−P_(SO), where p_(A) is the atmospheric pressure. 10.A method according to claim 9, characterized in that a membrane pump isused in which the suction connection is connected to the pumping chambervia a non-return valve, wherein the non-return valve is designed suchthat it opens when there is a pressure difference Δp_(SV) between thepressure at the suction connection and the pressure in the pumpingchamber, wherein the spring element is selected such that for thepressure p_(FV) applied to the working fluid by the spring element itholds that: p_(A)>p_(FV)>p_(A)−p_(SO)+Δp_(SV).